1. Field of the Invention
The present invention relates generally to pig valves, which are used for fluid flow control and for inserting pig devices, such as bullet shaped pigs, balls, scrapers and the like, into pipelines for internal cleaning, for separation of fluids within the pipeline and for other pipeline inspection and servicing activities. More particularly, the present invention concerns a rotatable ball type pig valve having universal type mounting flanges. The pig valve mechanism has a trunnion supported valve ball and incorporates seat members that are enabled to shift laterally within respective seat recesses and thus establish a self-centering characteristic with respect to the substantially spherical surface of a valve ball member during valve use.
2. Description of the Prior Art
Pig valves are regularly used for inserting pig devices into pipelines and retrieving the pig devices from the pipelines. Pig devices take a variety of different forms, such as “bullet pigs” of cylindrical configuration, with a rounded leading end, ball devices, scraper devices, and the like. Pig devices are passed through pipelines for the purpose of cleaning deposits, line scale and other foreign matter that might have accumulated within a pipeline or may have become adhered to the inner wall surface of the pipeline. Pigs are also used to separate a liquid or gas material from another liquid or gas material to prevent differing materials from becoming mixed as they flow through a pipeline. Certain pig devices are also run through pipelines for inspection of the structural integrity of the material from which a pipeline is composed.
Pig valves can be of various types, including ball valves, gate valves, rotary plug, valves. Pig launching and retrieving systems may include pig launchers, which are not valves, but which employ various types of valves to enable a pig member to be inserted into a pipeline. Pig traps are mechanisms that are mounted in communication with pipelines and which function to catch and secure a pig member after it has completed its passage through a pipeline.
An example of a ball type pig valve is set forth in U.S. Pat. No. 5,752,690 of Ellett.